1. Field of the Invention
The present invention relates to a head positioning apparatus for positioning a head on a disk-shaped recording medium with respect to which information is recorded or reproduced.
2. Description of the Related Art
In recent years, with the development of multimedia, in the market, there is a strong demand for a high-recording density disk apparatus capable of positioning a head at a targeted position at high speed and recording/reproducing a large capacity of video information, audio information and character information, and the like, at high speed. Since in particular, there has been an increasing demand for using a magnetic disk apparatus for mobile terminal apparatus, etc., it is necessary to further miniaturize the magnetic disk apparatus. As the disk apparatus is becoming smaller in size and higher in density, there has been an ever stronger demand for more accurate positioning of the head.
In particular, in accordance with the miniaturization of the disk apparatus, friction in a bearing portion, provided in a positioning mechanism for positioning a head, effects the driving control by an actuator, which substantially effects the positioning of the head. Since the effect of the friction on the positioning mechanism lowers the positioning accuracy, it raises an important problem as the disk apparatus is becoming smaller in size and higher in density.
The positioning mechanism by an actuator provided in the disk apparatus includes a linear actuator called a linear acting type and a rotary actuator called a swinging type. Both the linear actuator and rotary actuator are guided by a roller bearing portion.
A bearing portion constantly generates a friction force that is a reaction force with respect to a movement of a head support mechanism driven by an actuator. For example, when the actuator starts to be driven from a state in which the head support mechanism is stopped, the actuator is required to generate a driving force grater than the friction force based on the static friction between the bearing portion and the head support mechanism.
Furthermore, after the head support mechanism is started to move, friction force based on the dynamic friction acts between the bearing portion and the head support mechanism. In general, in order to move a movable portion such as a head support mechanism, the static friction needs larger driving force as compared with dynamic friction. Therefore, in the mechanism carrying out the moving operation using such a bearing portion, due to the difference between the static friction and the dynamic friction, a smooth moving operation becomes difficult, which may lead to an inaccurate positioning servo control.
Furthermore, since the bearing portion is miniaturized in accordance with the miniaturization of the disk apparatus, the effect of the friction force on the movement of the head support mechanism becomes more significant. Furthermore, since the head support mechanism also is smaller and lighter, similar to the friction force, for example, the reaction force generated due to the flexible printed circuit (hereinafter, referred to as FPC) for transmitting electric signals in a state in which it is connected to the head affects the movement of the head support mechanism significantly.
Thus, in accordance with the miniaturization of the disk apparatus, friction force of the bearing portion, reaction force of FPC and actuator vibration due to spindle vibration may inhibit the increase in recording density.
Then, in order to carry out the positioning of a magnetic head at high speed and with high accuracy, it is predicted that future general magnetic disks have a configuration including two driving mechanisms, i.e., a coarse actuator and a fine actuator.
The coarse actuator such as a voice coil motor (VCM) moves a head support mechanism, a slider and a magnetic head by rotating the head support mechanism around an axis provided at a chassis. The coarse actuator is mainly used for a long-distant movement such as seek/setting, a jumping a plurality of tracks, and the like.
The fine actuator drives a magnetic head or a slider. The fine actuator mainly is used for carrying out micro and high-speed positioning such as tracking or one-track jump, etc. The fine actuator also is referred to as a “micro actuator” (MA).
The magnetic head reads servo information recorded on a magnetic disk (information on the present position of the head). By controlling the coarse actuator and fine actuator, based on the servo information, a magnetic head mounted on the slider is allowed to access an arbitrary position on the magnetic disk so as to carry out positioning.
As compared with the conventional coarse actuator, the fine actuator can be control driven in high frequency zone and can carry out positioning of the magnetic head while suppressing the influence of the bearing friction.
A mechanism having a coarse actuator and a fine actuator is generally referred to as a Piggyback actuator or a dual-stage actuator or a dual stage actuator.
A controlling method having a configuration in which positioning at high speed and with high accuracy is carried out using this dual-stage actuator has been proposed. A conventional example of the control method using the dual-stage actuator will be mentioned below.
FIG. 24 is a block diagram showing a configuration of a servo control system in a dual-stage actuator described in JP4-368676A (U.S. Pat. No. 3,089,709).
In FIG. 24, a fine actuator G2 (S) carries out positioning of a head by feeding back a head position error (error between the targeted position and the position of the present position of the head) detected by a head signal; and a coarse actuator G1 (S) carries out positioning by feeding back a signal obtained by adding the displacement amount of the fine actuator G2 (S) to the head position error, thus achieving cooperative control.
Herein, the fine actuator G2 (S) is configured by a piezoelectric element and since the displacement amount is proportion to an input signal (input voltage) to the piezoelectric element, based on the input signal to the fine actuator G2 (S), the displacement amount of the fine actuator G2 (S) can be estimated.
Furthermore, a signal obtained by adding the displacement amount of the fine actuator G2 (S) to the position error corresponds to the position error between the targeted position and the position to which the head moves by the coarse actuator G1 (S).
According to such a control method, while control-driving the fine actuator G2 (S) in the middle of the operation range, by the cooperative control of the coarse actuator G1 (S) and the fine actuator G2 (S), positioning of the head is carried out with high accuracy.
FIG. 25 is a block diagram showing a configuration of a servo control system in a dual-stage actuator described in JP11-219572A (U.S. Pat. No. 3,180,752).
In FIG. 25, a head position error signal 25 detected from the head signal (error between the targeted position and the position of the present position of the head) and a relative position detection signal 26 representing the relative position between the coarse actuator and the fine actuator detected by a capacitor sensor are fed back to the input controller 29 and thus the positioning of the head is carried out with high accuracy by the cooperative control of a micro tracking actuator controller 30 and a main actuator controller 31.
According to such a control method, while control driving is carried out in the middle range of the operation range of the fine actuator, the positioning of the head is carried out with high accuracy by the cooperative control of the coarse actuator and the fine actuator.
However, in the configuration shown in FIG. 24, since the cooperative control of the coarse actuator G1 (S) and the fine actuator G2 (S) is carried out based only on the position error by the head signal, the amount of displacement of the fine actuator G2 (S) is added to the input signal of the coarse actuator G1 (S). Therefore, the fine actuator G2 (S) is subjected to the disturbance of the operation of the coarse actuator G1 (S); and the coarse actuator G1 (S) is subjected to the disturbance of the operation of the fine actuator G2 (S). As a result, residual vibration occurs, which may lead to an increase in the setting time in positioning the head.
Therefore, with the configuration in which the control zone of the fine actuator G2 (S) is made to be higher than the control zone of the coarse actuator G1 (S), when the operation of the fine actuator G2 (S) is allowed to be dominant, although it is possible to obtain an effect of improving the problem in which the settling time in positioning of head is increased, there still has been a problem in that the occurrence of the vibration due to the cooperative operation cannot be eliminated.
Furthermore, in the configuration shown in FIG. 25, in order to detect the displacement amount of the fine actuator to the coarse actuator, a capacitor sensor is added. Therefore, the configuration of the dual-stage actuator becomes complicated and simultaneously the mass and moment of inertia are increased by the added capacity sensor, and therefore, high speed seek and high frequency zone control cannot be achieved.